Railroad signaling devices are positioned at various locations along railroad tracks to provide information relating to the state of an upcoming stretch of track known as a block to locomotive operators. In particular, railroad signaling devices have aspects and indications that are interpreted by locomotive operators to adjust locomotive operation accordingly. The aspect specifies the type of railroad signaling device (e.g., absolute, permissive, etc.) and the indication specifies the state of the railroad signaling device (e.g., stop and stay, proceed, etc.). Typically, a railroad signaling device employs visual cues to present the aspect and the indication to a locomotive operator.
In one example, a color scheme is utilized to impart the status of a block to a locomotive operator with separate lights and lenses for each color, similar to that of road traffic signals. In another example, a light position scheme is utilized to impart the status of a block to a locomotive operator where the position of the lights, rather than their color, determines the meaning. In yet another example, a color-position scheme is utilized to impart the status of a block to a locomotive operator where the combination of color and position is used to determine the meaning.
However, due to the visual nature of all of these signal schemes, various situations may occur where the aspect and/or indication of a railroad signaling device is misinterpreted or missed completely. For example, a railroad signaling device may be misinterpreted due to poor visibility caused by weather conditions (e.g., fog, snow, rain, etc.), operator error caused by railroad personnel preoccupation, or the like. As another example, railroad signaling devices may be misinterpreted due to a lack of standardization. Railroad signal aspects/indications and physical signal types can vary greatly from one railroad company to another. Moreover, railroad signal aspects, indications, and physical signal types can vary greatly from one division to another within the same railroad company.
Furthermore, the issues associated with railroad signals that provide block status information visually may be compounded by the fact that railroad signals are located external to and uncoupled from the locomotive. This may create a distance limitation at which a locomotive operator may react to a block status that affects locomotive operation. Furthermore, upon passing a railroad signaling device, a locomotive operator has no way of knowing the status of a block in advance of the locomotive or the status of a block in behind the locomotive. Thus, in some situations, a collision may occur due to reverse movement of a locomotive resulting in the locomotive reentering a block.